The invention relates to a method of manufacturing a semiconductor device whereby a semiconductor body is provided at a surface with at least one groove which extends from the surface into the semiconductor body, a zone doped with an impurity being provided in a portion of the groove by means of ion implantation through a mask. The invention also relates to a semiconductor device manufactured by such a method.
The groove, which may have, for example, a U- or V-shape, may form a separation region between active regions, such as an island insulation in bipolar circuits. In an alternative embodiment, a conducting layer is provided in the groove, forming a gate electrode of a charge-coupled device such as described in, for example, the European Patent Application EP 0 239 151 filed by Applicant and laid open to public inspection on Sep. 30, 1987. In this device, the transport channel is situated in a mesa limited by two parallel grooves, the charge transport taking place along the walls of the mesa. Zones are formed locally in the walls, defining the charge storage locations in the channel.
U.S. Pat. No. 4,466,178 describes a method by which groove walls are doped by oblique implantation. In this method, doped zones are provided over the entire length of the grooves. It is often desirable, however, to provide the walls and/or the bottom of the groove or grooves only locally with doped zones which are provided over only a portion of the groove length.
Major practical drawbacks are involved, however, in the local implantation, i.e. not covering the entire groove length, of doped zones in narrow grooves which are relatively deep compared with their width. An obvious method is to use an implantation mask of photoresist. The realisation of a well-defined photoresist mask which leaves exposed only a portion of the groove bottom in a groove having a width of, for example, 2 microns or less and a depth of more than 3 microns is practically impossible. To illuminate the photoresist down to the groove bottom would require such a great illumination dose that the mask definition near the surface 7/uld become very bad, while the photoresist in the bottom of the groove would not or insufficiently be illuminated in the case of smaller illumination doses.
A method of the kind described in the opening paragraph is known from U.S. Pat. No. 4,756,793. In this known method, the grooves are temporarily filled up with a filler material, for example photoresist, so that an at least substantially plane surface is obtained. On this surface is provided an implantation mask of metal, for example Al, which has one or several openings where in a subsequent step the dopant is to be provided in the groove or grooves. The filler material is then removed from the groove or grooves at least at the areas of the windows in the implantation mask, or from the entire groove or grooves, upon which the implantation is carried out through the 7indows in the implantation mask. The implantation mask is then removed again.